Manmohan Singh's reign as Prime Minister has been severely criticised by his former ministerial colleague Natwar Singh, who says he leaves no legacy after being in power for 10 years.

Singh, who was External Affairs Minister under Manmohan Singh, says the MEA was "demoralised" since it was run from the prime minister's office.

"What will be history's verdict on Dr Manmohan Singh's prime ministership? It will either be benignly indifferent or reduce it to a mere footnote. What will be Manmohan Singh's legacy? Sadly, there will be none," he writes in his just-released autobiography 'One Life is Not Enough'.

Singh was External Affairs Minister in UPA-I and he had to resign after his name appeared in the Iraqi oil-for-food scam in 2006.

Quoting Winston Churchill's famous 'The morning was gold, the afternoon was silver, the evening lead' take on Lord Curzon, Singh says Manmohan's tenure could be similarly described.

"He (Manmohan) forgets no slight but is an expert at camouflaging his emotions," he writes.

"As far as Manmohan Singh's foreign policy was concerned, he didn't have one... Matters were made worse when the Prime Minister sent a former Cabinet minister to Japan as a special envoy, even though we had a senior Ambassador in Tokyo," he writes.

There was a broad national consensus on foreign policy till Manmohan Singh became Prime Minister, he says, adding that he leaned "backwards to accommodate the US, even when they displayed indifference".

"India did not utter a word against the US's spying over a large number of countries, including India. What else could one expect from a Prime Minister who once told President George Bush, 'Mr President, the people of India dearly love you.' Which Indians did he have in mine?," Singh writes.

"Even with our neighbours, our relations were not what they should have been," he says.

He has also suggested in his book that Manmohan was not comfortable with Sonia Gandhi wielding the power she did over the government.

"On 31 July (2004), Manmohan Singh asked me to see him, if I was free. I was, so I went up to his sixteenth-floor suite at the hotel. He said he was a very lonely man. He seemed to suggest that the present arrangement to have a dyarchy was unsatisfactory.

"We discussed state matters, after which I told him that he was the best man for the job and he had Sonia's full confidence. 'We are all with you,' I assured him," Singh